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  #1  
Old 11-09-2009, 05:23 PM
aviator_edb aviator_edb is offline
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Default Dark specs in the layup

I've been doing additional practice layups becuase my first seatback came out looking like the photo and it's starting to make me insane.

I keep getting these "bubbles" in my practice layups.

If you zoom in on the photo and look about the ruler you'll see what I am talking about. Are these dark spots air bubbles? I've got a very small number (less than 0.5 in^2 TOTAL) of other bubbles that I'm sure ARE air. They are much lighter in color.

This is the 1 ply of BID done on the back of the seatback.


Sorry for the large size. It's the only way to really see what I'm talking about..


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  #2  
Old 11-09-2009, 10:41 PM
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Default Re: Dark specs in the layup

Well, if in fact it is air then you may be squeezing it in.

Call me, easier by phone.
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  #3  
Old 11-10-2009, 09:42 AM
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Default Re: Dark specs in the layup

They look like air to me.

The Rutan booklet says if you have more than 10% bubbles, flecks, etc on any 6"x6" area, it is a reject part. You photo looks like a lot less than 10% flecks to me...

The three primary ways to get air in the layup like that are:

Your materials were not up to temperature before you started the layup. A good rule of thumb is to set the temperature of the room the day before. Foam can take a long time to warm up. If you start with cool foam, and then warm it up, air in the foam expands, bubbles form and then float out;

You did not fully fill the surface with micro before starting, leaving broken foam cells with air in them that then floats out;

You drove the air in by trying to work epoxy into the layup, which does not really work anyway.

It also looks as if you might have more micro slurry on the foam and more epoxy on the cloth than you should. Proper squeegee technique works well here. Remember, light passes. And when you think that you have removed enough resin, make a light pass, then stop the squeegee and lift. If a ridge remains, there is still excess epoxy.

Some hints (Dust will probably cover some of these)(the Rutan booklet covers these pretty well too):

Work the micro on the foam several times with a squeegee. Make sure that you have the broken cells filled and then have squeegeed the excess micro from the part. If a squeegee pass is still making pops and crackles, you are not done yet - those are bubbles being broken that may require more slurry before they are done;

Lay on the cloth, get the fibers straight, and then wet the cloth with epoxy. Wet the whole part as quickly as you can and spread and work the epoxy with a squeegee wherever you can. You are trying to get the hot epoxy spread out and soaking into the cloth everywhere as early in the process as possible;

Then, with big squeegee strokes (in the directions of the fibers and in full dimensions of the part), you work the epoxy. This drives the first layer of cloth into intimate contact with the foam or cloth below it, pulls fibers tight, and gives you the opportunity to remove air and then excess epoxy. Again, if you hear pops and crackles, you still have more passes to make over the entire part before removing excess epoxy;

If you can not get the bubbles, a hair dryer to gently warm the region you are trying to get bubbles out of will enlarge the bubbles and lower the resin viscosity, allowing them to exit. Remember - gentle heating, only a few degrees, which you can do with a simple pass or two, then more squeegee...

Don't ever allow yourself to sit and concentrate on one spot. If it is not wet out, sweep some epoxy over the area and move on.

The big piece of wisdom to be obtained is that no amount of sitting and working a spot will drive epoxy into the cloth any faster than just spreading epoxy and going somewhere else on the part. And it can drive air into the part... So, spread epoxy and move on. By the time you cycle over the whole part and get back there, it will have soaked in, and now needs to be squeegeed down and the excess epoxy (with air in it) is carded off.

There is one more technique that I have to show to folks who help me. They try to sweep epoxy to the edge of the part with the squeegee. It works OK with micro, but not so good with cloth and frequently sweeps epoxy off the part. Instead, just pick up a bit of excess epoxy with a sweep of the squeegee, then take the squeegee to the edge of the part, and draw the squeegee towards the middle. This spreads just about the right amount of material on the dry edge and picks up a new bit of epoxy in the center. You can just work your way along the edge placing the squeegee on the edge and drawing toward center repeatedly. By the time you get to the starting point, it will be wet enough to tell if it needs a little more epoxy or if you can start working the cloth down and remove excess epoxy.

One last thought. Get a fluorescent trouble light for doing your inspection work. Incandescent lights and big work lights heat the surface and create more bubbles in the layup, which is what you are trying to avoid...

Billski
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Old 11-12-2009, 12:49 PM
aviator_edb aviator_edb is offline
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Default Re: Dark specs in the layup

Bill and Mike,
I've been doing some scap practice layups and notices something. I think its me squeeging. I think I'm doing it too much and way to hard.

Many of my small practice piece come out looking fine but when I did the big pieces things got ugly. Whats the big difference? For one, on the bigger pieces you have to mix more epoxy and wet out a much larger area.I think I'm trying to spread out the eppoxy too much and WORK it in instead of letting things soak in on their own while I mix the batch.

In reading chapter 3, watching the Rutan video and other resoruces they all say to not spend too much time on one place until you have the whole part wetted out. Then go back and with LIGHT passes of the squeegie make your adjustments.

I need to remember that I'm using SLOW hardener and I have PLENTY of time. Mix it up, Dump it on, lightly spread it out, repeat. Get the whole piece covered THEN go back over and work out any remaining air and fianlly take off the excess epoxy with, again, LIGHT squeeging.

Mike, if you have time I'd appreciate the chance to speak to someone about this. It is hard to describe and discuss stuff like this ona forum. We can sort out contact detail on PM

thanks guys.
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Old 11-12-2009, 01:51 PM
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Default Re: Dark specs in the layup

nearly always have a canardian moment, if i don't i'll just tell you "later"

this is my practice, dump and spread on first layer, make sure all is over wet, place second layer, if this is the last layer add heat and squeege and add epoxy as needed, if not the last layer, same as the first.

my object is to have the last layer pull excess from bottom. this works for about 4 or 5 layers
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  #6  
Old 01-07-2010, 04:57 AM
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schmeddz schmeddz is offline
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Default Re: Dark specs in the layup

Those are air bubbles in the foam/slurry layer. Those are below the glass layer and on top of the foam and slurry. Not a problem for the sizes and spacing. They usually come up out of the foam slurry layer after you wet out the glass layers. Unless you want to wait after you slurry the foam for a awhile for the bubbles to come up and re-squegee the slurry, I wouldn't worry about it. The glass work looks good although there is a bit too much resin on the surface where you don't see the fiberglass weave.
The 10% Rutan spec is if it's over 10% of the surface area. That's not even close.

Last edited by schmeddz : 01-07-2010 at 05:07 AM.
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